Tapping of metals



R. PERRIN TAPPING OF METALS Filed Oct. 17, 1939 June 17, 1941-.

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Patented June 17, 1941 dElectrochimie,

Ren Perrin, Paris, France, assignor to Societe dElectrometallurgie et des Acieries Electriques dUgine, Paris, France, a v corporation of France Application October 17,1939, Serial No. 299,865

- In France October 17, 1938 6 Claims. (01. 266-37) In many steel metallurgy processes it is advantageous and often necessary, at a given stage of such processes, to separate as'completely as possible the metal bath from theoverfioating slag;

this is particularly the case when it is necessary .to separate the metal from the slag just at the time of pouring, i; e; to pour allthe metal ofthe furnace without a substantial entrainment of the slag together with the metal. This problem is particularly important when after tapping of the furnace dephosphorizing, deoxidizing, desulphurizing or any other reaction on liquid steel is to be carried out in a ladle by treatment with solid or. liquid slags placed in the said ladle, or even simply when a subsequent reaction between slag and metal is to be avoided-for instance in controlling the MacQuaid grain size of the steel according to-the process disclosed in U. S. Patent No. 2,087,580.

Such a separation between slag and metal, at the time of pouring, may be rather easily performed in the case of tilting furnaces, such for off of the bath, by means of scrapers, without mentioning the undue strain that such a work causes to the workmen. Practice shows that when pouring Martin furnaces, a relatively high amofint'of slag passes at the same time as the metal,'especi ally in the last third part of pouring and the said amount is so much higher for the same form of furnace as the tapping hole becomes larger and the pouring more rapid.

The present invention provides a simple, economical means, not causing any special'strain to workmen, for practically preventing such simultaneous passage of metal and slag through the tapping hole and insuring that the slag is poured only after the metal. Furthermore if at that time the passage of the slag takes place it cannot trouble the reactions eventually performed in the ladle since the metal and the said slag would not then be sufliciently mixed together that the latter may exert a noxious action.

Considering what happens in pouring a Martin furnace, especially in the last part of pouring, it will be ascertained thatnear the tapping hole there is, formed in the slag and in the metal a real vortex similar to those noticed when discharging water from the bottom of a wash-stand; the overfloating slag is entrained within the said vortex together with the metal. The formation of the said vortex is particularly due to the unequal velocity of the various fluid streams, being themselves unequally braked, particularly on account of friction against the furnace walls and the tapping hole. After having attended some pourings, it will be easy to exactly locate the place in the furnace where the said vortex is formed. Its size is substantially constant provided that the size of the tapping holeis maintained approximately regular. I

The present invention consists in floating on the metal or in the slag a little distance above the metal at the place where the vortex would normally be formed a plate. or, raft which is maintained at said place on the'metal surface and which is allowed to lower or is lowered together with the metal. Such a raft practically drives away the slag from the vortex space or at least prevents it from being entrained by the metal when pouring takes place; on the other hand it considerably reduces the intensity of formation of such vortex or even prevents its generation by causing supplementary frictions. The weight'of the raft as well as the force eventually applied to it, where force is used, are advantageously so deis automatically secured by the'presence of the.

raft itself.

The insertion of the raft may be performed either at the beginning of pouring or more advantageously during the last part of pouring, when its presence is particularly useful.

The external contour of the raft is determined in each particular case by observing the-size and shape of the vortex and the forfifof the furnace lining, so that the raft will occupy and largely cover the space where the vortex would otherwise be formed, It is advantageous in practice to have the part of the raft proximate to the furnace wall, substantially follow the contour of such wall. It is also advantageous to adapt the form of saidraft to the wear of the lining throughout the season.

The raft may simply be placed on the bath surface by means of a Martin furnace charging machine or any other device and left to itself, only guiding it during the pouring by means of rods,

if, on account of the motions of the bath, it tends to divert from its normal position.

The raft may also be permanently carried by any kind of appropriate support, for instance a metal shaft, cooled by water circulation and linked in such a way that the raft may freely follow the metal in its descent under the action of its gravity and also of the gravity of the rod itself, the latter being, if desired, totally or partially balanced by a counterweight.

The raft may also be constituted by several parts, linked to one another, for instance by means of asbestos joints in order that it may more easily follow at the end of the pouring the form of the section of the lower part of the furnace. It may for instance be constituted by means of one or more wood trays or joists, which may or may not be linked together. Such wood parts may, if desired, be bound by an iron fitting. Such fitting may also be simply recessed into the 'wood raft. When pouring is completed or nearly completed, and the slag itself is flowing through the tapping hole the raft may be removed from the furnace and set aside so that the discharge of the slag will not be restrained. The raft may be used again, after cleaning, for a subsequent treatment or simply left in the furnace if it is constituted of a material which is combustible or soluble in the bath or in the slag.

When araft made of wood is positioned, some gas evolution takes place and tends to drive away the slag and to cool it, this being advantageous. There is a slight combustion of the wood, but this is without importance; the resulting carbonizing of the metal bath is absolutely unimportant. The wood may of course'be replaced by graphite, electrode fragments, or like material as well as by ,non combustible refractory materials.

An embodiment of the invention is shown by way of example in the accompanying drawing.

In said embodiment, which corresponds to a furnace comprising a front wall I, a hearth 2, a tapping hole 3 and a charging aperture 4 provided with a door 5 which due to its vertical movements is capable of closing or opening, ac-

cording to its position, the charging opening 4; the tapping hole 3 is closed by a plug 6 which retains the metal bath 1 on which the slag 8 is floating. The removal of the plug 6 and the resulting flow of the contents of the furnace, cause in normal flowing conditions a vortex 9 diagrammatically shown in chain and dotted lines, on account of which a given amount of the slag 8 flows together with the metal before its upper surface reaches the level AA which corresponds to the upper part of the tapping hole. In order to avoid the formation of said vortex and consequently the entrainment of the slag together with the metal, according to the invention a raft I 0, for instance of wood fitted with iron, is placed at the point at which the said vortex would normally be formed, the said raft I0 being secured by means of a metal flange II to a supporting shaft I2 on which it is pivoted means of the flywheel 22 carrying a pinion 23 engaging a rack 24 supported by the beam I 4.

The operation of the apparatus thus constituted is as follows: at the time of pouring or during such pouring, for instance towards its end, the door 5 is opened and the shaft I2 is introduced into the furnace by moving the carriage I6. The raft III is lowered by operating the crank pins 20 until it comes in contact or substantially in contact with the metal, thusdriving away the slag layer. By adjusting the position of the counterweight 2| on the beam I4 to substantially balance the weight of the particular raft and its supportingshaft, only a small force need be applied to the crank pins 20 to lower or raise the raft. As the pouring proceeds, the aft is lowered by operating the crank pins 20 insuch manner that the raft remains substantially in contact with the metal. A vortex 9 cannot thus be formed and no slag or a very small amount of slag flows until 'the upper surface of the metal bath reaches the level A-A above the tapping hole 3. At such a time the remaining metal and slag may be fed into another ladle. When using the type of apparatus shown in the drawing the raft may be taken out by lifting the shaft l2 and removing the carriage IS. The raft is then again ready for use or if it has been partially worn out by the treatment it may be repaired according to its wear or replaced by a new raft.

It is not necessary that the bottom of the raft be completely closed. It can contain openings and nevertheless fulfill its function of preventing or decreasing the formation of a vortex with the consequent entrainment of slag. The formation of a vortex in the metal and slag depends on many circumstances, e. g. the depth of the bath, the velocity of tapping, the area of the tapping opening-the viscosities of the metal and of the slag, the location of the tapping opening with regard to the walls ofthe furnace or receptacle, etc.

When the velocity of the tapping is very great and the depth of the bath is small, a vortex is immediately formedrbut when the velocity of the tapping is smalland the depth of the bath is,

great, it may happen that no vortex is formed as long as the depth of the bath remains important. Again when the velocity of the tapping is very small, a vortex may be formed only at the very last part of the tapping. 0n the other hand, the greater the velocity ofthe tapping, the greater is the vortex and vice versa.

When a large and deep vortex would be formed in the absence of the raft, a completely closed bottom is necessary for the raft to prevent the formation of a vortex. On the contrary, when the vortex would be small and not deep in the absence of the raft, a raft which does not have a completely closed bottom can be used. The degree of closure of the bottom of the raft can not be given by figures on account of the many by the axis I3. The shaft I2, which in the embodiment shown is hollow and provided with water circulation is fixed to a beam I4 pivoted to.

an axis I5 supported by a carriage I6 moving on the service platform ll of the furnace. A toothed sector I8, secured to the beam I4 and engaging a pinion I9 enables by acting on such pinion by means of the crank pins 20, to lift or to lower the shaft I2. A counterweight 2|, sliding on the beam I4, may be moved along said beam by variable circumstances above referred to.

closed bottom.

What I claim is;

1. Process for preventing when tapping ofl a molten metal covered with a layer of slag the entrainment of slag with the metal, consisting in placing on the metal substantially in contact with said metal at the place where a vortex would be-normally formed during the tapping, a raft having a substantially closed bottom extending over the said place.

2. Process for preventing when tapping oif a molten metal covered witha layer of slag the entrainment of slag with the metal, consisting in placing on the metal at the place where a v vortex would normally be formed durin the tapping oil, a raft having a substantially cosed bottom and which is too light for substantially dipping into the metal, and exerting a vertical pressure on the said raft for causing it to substan tially dip into the metal.

3. An apparatus for preventing during the pouring of 'a molten metal covered with slag the entrainment of said slag, consistingin a raft which is sufficiently broad in every horizontal direction to cover the place where a vortex'would normally be formed during the tapping off of the metal bath, said raft having a substantially 4. An apparatus for preventing during the tapping off of a molten metal covered with a layer of slag the entrainment of said slag, consisting in a raft which is sufllciently broad in every horizontal direction to cover the place where a vortex would normally be formed during the tapping of! of the metal bath, and which is given on its edge facing the wall of the furnace substantially the shape of said wall, said raft having a substantially closed bottom.

5; In an apparatus for preventing during the tapping of! of a molten metal covered with slag the entrainment of said slag, a raft having a substantially closed bottom, said raft made of a material which is sufflciently resistant to destruction by fire to cover substantially until the end of the tapping of! the place at which a vortex would normally be formed and suspended at one end of a hollow metal shaft, circulated by a cooling fluid and which is pivoted on a displaceable carriage, and a mechanism displacing downwards and upwards the said hollow metal shaft.

6. Process for preventing when tapping oil a molten metal covered with a layer of slag the entrainment of slag with the metal, consisting in placing on the metal at the place where a vortex would normally be formed during the tapping 011',

a raft having a substantially closed bottom extending over the said lace and, as tapping off proceeds,. maintaining the raft at substantially a constant depth with respectto the level of the molten metal and in register with said place where a vortex would normally be formed.

RENE PERRIN. 

